1. Field of the Invention
The present invention relates to a remote-control unit for vehicles that is installed in a mechanical key (hereinafter, simply, a key) and used to transmit a dedicated cipher system code and ID code, and cooperates with a vehicle control system installed in a vehicle in controlling the door lock of a vehicle to be operated remotely and in permitting engine start, and to a vehicle security system.
2. Description of the Related Art
In recent years, a case of theft of a motorcar has tended to a marked increase, and realization of a theft prevention system capable of ensuring high security has been demanded.
Various realizations including a remote-control unit for vehicles that unfastens the door lock of a vehicle through remote control, a remote-control unit for vehicles that communicates with a vehicle using a cipher system code for the purpose of preventing theft of the vehicle, and a vehicle security system using such a remote-control unit for vehicles have been proposed in the past.
For example, a known immobilizer designed for preventing theft (illegal engine start prevention system) is such that: an engine is not started merely by fitting a key into a key cylinder for starting an engine; only when an ID code sent from a circuit in the key agrees with an ID code stored in a control unit inside a vehicle, the engine is started; and when both the ID codes disagree with each other, engine start is inhibited.
In a known keyless entry system for fastening or unfastening a door lock through a remote-control operation, unless a key having a built-in remote-control unit transmits a given cipher system code to a vehicle control unit, the door lock is, for example, not unfastened.
FIG. 12 is a block diagram schematically showing the configuration of a known vehicle security system described in, for example, Japanese Unexamined Patent Publication No. 8-86130, illustrating a vehicle security system having an immobilizer facility for judging from information to be communicated between a key and vehicle whether or not starting an engine may be permitted.
In FIG. 12, the vehicle security system functioning as an immobilizer system comprises a transponder 11A in which an ID code for use in preventing illegal engine start is written, a key 10 having the transponder 11A incorporated therein, a coil antenna 20 located in a vehicle (not shown), a key cylinder 21 having the coil antenna 20, a vehicle control unit 30A including a microcomputer mounted in the vehicle, and an engine control unit 29 to be controlled by the vehicle control unit 30A.
The vehicle control unit 30A includes a control circuit 25 formed with a CPU for responding to handling of the key 10 in the key cylinder 21, and processing transmitted data or received data, an EEPROM (electrically erasable PROM) 26 serving as a memory means for the control circuit 25, an engine communication assistance circuit 28 inserted between the control circuit 25 and engine control unit 29, and a radio-frequency transmission/reception circuit 23A inserted between the control circuit 25 and coil antenna 20.
The vehicle control unit 30A operates with power supplied from a vehicle battery 34.
Normally, when the key 10 is fitted into the key cylinder 21, a mechanical switch operates so that a key detection signal K is produced and input from the key cylinder 21 to the control circuit 25. This causes the control circuit 25 to recognize the handling for fitting the key 10 and transmit a specific ID code from the radio-frequency transmission/reception circuit 23A to the transponder 11A.
In response to the ID code, the transponder 11A transmits the specific ID code to the coil antenna 20.
The radio-frequency transmission/reception circuit 23A in the vehicle control unit 30A inputs the ID code, which has been received from the transponder 11A in the key 10 via the coil antenna 20, to the control circuit 25.
The control circuit 25 compares the received ID code with an ID code stored in advance in the EEPROM 26, and thus judges whether or not starting the engine should be permitted. Thus, it is prevented that the engine is started with another person's key, and theft can be prevented.
As shown in FIG. 12, the immobilizer system comprising the key 10 having the transponder 11A incorporated therein and the vehicle control unit 30A for communicating with the key 10 via the coil antenna 20 enjoys improved cost performance owing to the configuration thereof realized by uniting a key entry system for remotely unfastening the door lock using the transponder 11A, an immobilizer for preventing theft, and a theft-prevention alarm system.
FIG. 13 is a block diagram schematically showing the configuration of a known vehicle security system described in, for example, Japanese Unexamined Patent Publication No. 8-149127, illustrating a vehicle security system having a keyless entry facility for opening or closing a door lock or unlocking a trunk through communication.
In FIG. 13, components identical to those in FIG. 12 are assigned the same reference numerals. The description of the components will be omitted.
This vehicle security system based on a keyless entry system comprises a remote-control unit 11B for vehicles having a CPU incorporated in the key 10, a vehicle control unit 30B including a reception antenna 22, and a door lock control unit 31 to be controlled by the vehicle control unit 30B.
The remote-control unit 11B for vehicles in the key 10 consists of a manual switch 12 to be handled by a user for activating a keyless entry facility and thus opening the door lock, a compact battery 13 for supplying power to a CPU in the remote-control unit 11B for vehicles, a control circuit 14 that is the CPU to which power is supplied from the battery 13, a transmission circuit 15 for transmitting various cipher system codes CS to the antenna 22 in the form of a radio wave under the control of the control unit 14, and an EEPROM 17 serving as a memory means for the control circuit 14.
In the EEPROM 17 in the remote-control unit 11B for vehicles, different ID codes associated with individual keys 10 and different cipher system codes CS associated with respective communication operations are stored. The data of these cipher system codes CS is retrieved by the control circuit 14 for each transmission.
The vehicle control unit 30B includes a reception circuit 23 for receiving an ID code and cipher system code CS transmitted from the remote-control unit 11B for vehicles, a control circuit 25 for controlling the door lock control unit 31 in response to received data, an EEPROM 26 belonging to the control unit 25, and an input/output interface 27 inserted between the control circuit 25 and equipment mounted in a vehicle.
The input/output interface 27 is connected to a lamp 32 in a room of the vehicle and to a door 35 of the vehicle, and drives the lamp 32 according to the ON or OFF state of an open/close switch for the door 35 under the control of the control circuit 25 so that the lamp 32 lights up to indicate that the door 35 is open.
The vehicle security system shown in FIG. 13 transmits the data of a cipher system code CS in the form of a radio wave (or infrared) from the transmission circuit 15 in the remote-control unit 11B for vehicles to the reception circuit 23 in the vehicle, and communicates with the door lock control unit 31 in relation to opening or closing of the door lock or unlocking of the trunk.
In this case, the code number of a cipher system code CS is modified in order to interfere with interpretation. Thus, the theft prevention facility is further guaranteed.
However, in the aforesaid vehicle security systems, the immobilizer system (See FIG. 12) and keyless entry system (See FIG. 13) are constructed independently but do not link up mutually. For realizing both the immobilizer and keyless entry facilities, the immobilizer and keyless entry systems must be installed independently.
This requests motorcar manufacturers to preserve places in which on-vehicle equipment are mounted to materialize the immobilizer and keyless entry systems. Besides, the number of connection lines increases. Consequently, the cost required for mounting the equipment increases. As for maintenance, it is obliged to assign labor separately to the equipment.
It is conceivable to utilize unidirectional transmission of a radio wave, which is a constituent feature of the keyless entry system, in common for the immobilizer facility. For permitting engine start (lifting inhibition of engine start), keyless entry handling or handling by which the keyless entry facility is activated must be carried out by a user without fail. Moreover, unless an engine is started within a predetermined period of time, another keyless entry handling become necessary. The idea is therefore not practical.
As for unidirectional transmission achieved by the keyless entry system, a method in which transmitted data (cipher system code CS) is fixed every time cannot reliably prevent interception and interpretation.
Moreover, by merely increasing or decreasing the numerical value of transmitted data, interception and interpretation of the transmitted data or copying thereof cannot be prevented reliably. An engine may be started illegally, thus causing vehicle theft or the like.
Furthermore, even if a circuit having both the capabilities of a simple transmitter receiver (transponder 11A) included in the immobilizer system described in the Japanese Unexamined Patent Publication No. 8-86130 (See FIG. 12) and of the transmission circuit 15 in the keyless entry system (See FIG. 13) is incorporated in a key 10, cost equivalent to the cost required for simply combining the keys 10 shown in FIGS. 12 and 13 is needed. Any merit is therefore not expected cost-wise.
In the known remote-control units for vehicles and vehicle security systems, as described previously, the immobilizer and keyless entry facilities are materialized as independent units but do not link up with each other. Assuming that the facilities are simply combined, if an engine is, for example, started, keyless entry handling must be carried out without fail. This poses a problem that security, handling efficiency, and cost-performance cannot be improved fully.